Use a TextFormula to return all multiple choice in one field

I hope this makes sense :)

I have a connection text field where we can enter staff initials against a single ticket. I have run into issues when exporting the data as the comma between the multiple choice is identified by my program as a delimiter in the CSV.

To get around this issue I would like to create a new field that will return the multiple choices as a single text string:

CP, AB, XY becomes CPABXY

I have tried using a text formula to return the value of the field but it is blank. (I'm also not sure why it gives the example of emin=emin above the formula - what does emin mean?)

Many thanks in advance for any guidance